Method for disconnecting a d2d link connection in a communication system and device therefor

ABSTRACT

The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device for disconnecting a device to device (D2D) link connection in a wireless communication system. According to an aspect of the present invention, the method comprising: establishing a radio resource control (RRC) connection with a cell; transmitting, to the cell connected with the remote UE, a reporting message on the D2D link connection; if the cell connected with the remote UE and a cell connected with the relay UE are different, receiving, from the relay UE, a first request message for disconnecting the D2D link connection with the relay UE in response to the reporting message; and disconnecting the D2D link connection according to the first request message.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method for disconnecting, by a remote userequipment (UE), a device to device (D2D) link connection with a relay UEin a wireless communication system and a device therefor.

BACKGROUND ART

As an example of a mobile communication system to which the presentinvention is applicable, a 3rd Generation Partnership Project Long TermEvolution (hereinafter, referred to as LTE) communication system isdescribed in brief.

FIG. 1 is a view schematically illustrating a network structure of anE-UMTS as an exemplary radio communication system. An Evolved UniversalMobile Telecommunications System (E-UMTS) is an advanced version of aconventional Universal Mobile Telecommunications System (UMTS) and basicstandardization thereof is currently underway in the 3GPP. E-UMTS may begenerally referred to as a Long Term Evolution (LTE) system. For detailsof the technical specifications of the UMTS and E-UMTS, reference can bemade to Release 7 and Release 8 of “3rd Generation Partnership Project;Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), eNode Bs(eNBs), and an Access Gateway (AG) which is located at an end of thenetwork (E-UTRAN) and connected to an external network. The eNBs maysimultaneously transmit multiple data streams for a broadcast service, amulticast service, and/or a unicast service.

One or more cells may exist per eNB. The cell is set to operate in oneof bandwidths such as 1.25, 2.5, 5, 10, 15, and 20 MHz and provides adownlink (DL) or uplink (UL) transmission service to a plurality of UEsin the bandwidth. Different cells may be set to provide differentbandwidths. The eNB controls data transmission or reception to and froma plurality of UEs. The eNB transmits DL scheduling information of DLdata to a corresponding UE so as to inform the UE of a time/frequencydomain in which the DL data is supposed to be transmitted, coding, adata size, and hybrid automatic repeat and request (HARQ)-relatedinformation. In addition, the eNB transmits UL scheduling information ofUL data to a corresponding UE so as to inform the UE of a time/frequencydomain which may be used by the UE, coding, a data size, andHARQ-related information. An interface for transmitting user traffic orcontrol traffic may be used between eNBs. A core network (CN) mayinclude the AG and a network node or the like for user registration ofUEs. The AG manages the mobility of a UE on a tracking area (TA) basis.One TA includes a plurality of cells.

Device to device (D2D) communication refers to the distributedcommunication technology that directly transfers traffic betweenadjacent nodes without using infrastructure such as a base station. In aD2D communication environment, each node such as a portable terminaldiscovers user equipment physically adjacent thereto and transmitstraffic after setting communication session. In this way, since D2Dcommunication may solve traffic overload by distributing trafficconcentrated into the base station, the D2D communication may havereceived attention as the element technology of the next generationmobile communication technology after 4G. For this reason, the standardinstitute such as 3GPP or IEEE has proceeded to establish the D2Dcommunication standard on the basis of LTE-A or Wi-Fi, and Qualcomm hasdeveloped their own D2D communication technology.

It is expected that the D2D communication contributes to increasethroughput of a mobile communication system and create new communicationservices. Also, the D2D communication may support proximity based socialnetwork services or network game services. The problem of link of a userequipment located at a shade zone may be solved by using a D2D link as arelay. In this way, it is expected that the D2D technology will providenew services in various fields.

DISCLOSURE Technical Problem

Based on the above-mentioned discussion, methods for disconnecting, by aremote user equipment (UE), a device to device (D2D) link connectionwith a relay UE and apparatuses therefor shall be proposed in thefollowing description.

Technical tasks obtainable from the present invention are non-limited bythe above-mentioned technical task. And, other unmentioned technicaltasks can be clearly understood from the following description by thosehaving ordinary skill in the technical field to which the presentinvention pertains.

Technical Solution

The object of the present invention can be achieved by providing amethod for disconnecting, by a remote user equipment (UE), a device todevice (D2D) link connection with a relay UE in a wireless communicationsystem, the method comprising: establishing a radio resource control(RRC) connection with a cell; transmitting, to the cell connected withthe remote UE, a reporting message on the D2D link connection; if thecell connected with the remote UE and a cell connected with the relay UEare different, receiving, from the relay UE, a first request message fordisconnecting the D2D link connection with the relay UE in response tothe reporting message; and disconnecting the D2D link connectionaccording to the first request message.

In another aspect of the present invention provided herein is an UEconnected with a relay UE through a device to device (D2D) link in awireless communication system, the UE comprising: a radio frequency (RF)module configured to transmit/receive signals; and a processorconfigured to process the signals, wherein the processor is configuredto establish a radio resource control (RRC) connection with a cell,control the RF modul to transmit, to the cell connected with the remoteUE, a reporting message on the D2D link connection, if the cellconnected with the remote UE and a cell connected with the relay UE aredifferent, control the RF modul to receive, from the relay UE, a firstrequest message for disconnecting the D2D link connection with the relayUE in response to the reporting message, and disconnect the D2D linkconnection according to the first request message.

Preferably, the RRC connection with the cell is established when aquality of a channel between the remote UE and the cell is higher than athreshold value.

Preferably, the reporting message including at least one of an identityof the remote UE, an identity of the relay UE, an identity of the cellconnected with the relay UE, an indicator indicating whether todisconnect the D2D link connection, an indicator indicating whether theremote UE is currently served by the relay UE and serving cell qualityof the remote UE.

Preferably, the method further comprising: if the cell connected withthe remote UE and the cell connected with the relay UE are same,receiving a first disconnection message, from the cell connected withthe remote UE, for disconnecting the D2D link connection in response tothe reporting message; and disconnecting the D2D link connectionaccording to the first disconnection message.

Preferably, the first request message is transmitted from the relay UEbased on a second disconnection message on the cell connected with therelay UE, and the second disconnection message is transmitted from thecell connected with the relay UE to the relay UE based on a secondrequest message on the cell connected with the remote UE.

Preferably, the second request message is transmitted from the cellconnected with the remote UE to the cell connected with the relay UE,and the second request message includes an identity of the remote UE andan identity of the relay UE.

Preferably, the second disconnection message includes an identity of theremote UE.

Advantageous Effects

According to the present invention, the UE can disconnect a device todevice (D2D) link connection with a relay UE in a wireless communicationsystem.

It will be appreciated by persons skilled in the art that that theeffects achieved by the present invention are not limited to what hasbeen particularly described hereinabove and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention.

FIG. 1 is a diagram showing a network structure of an Evolved UniversalMobile Telecommunications System (E-UMTS) as an example of a wirelesscommunication system;

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS), and FIG. 2B is ablock diagram depicting architecture of a typical E-UTRAN and a typicalEPC;

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3rd generationpartnership project (3GPP) radio access network standard;

FIG. 4 is a diagram of an example physical channel structure used in anE-UMTS system;

FIG. 5 is an example of default data path for a normal communication;

FIGS. 6 and 7 are examples of data path scenarios for a proximitycommunication;

FIG. 8 is a conceptual diagram illustrating for a non-roaming referencearchitecture;

FIG. 9 is a conceptual diagram illustrating for a Layer 2 Structure forSidelink;

FIG. 10a is a conceptual diagram illustrating for User-Plane protocolstack for ProSe Direct Communication, and FIG. 10b is Control-Planeprotocol stack for ProSe Direct Communication;

FIG. 11 is a conceptual diagram illustrating for a PC5 interface forProSe Direct Discovery;

FIG. 12 is a conceptual diagram illustrating for one example of awireless Communication system supporting ProSe Direct Communicationaccording to one embodiment of the present invention.

FIGS. 13-15 show an example of a method for disconnecting a D2D linkconnection according to an embodiment of the present invention.

FIG. 16 is a block diagram for one example of a communication deviceaccording to one embodiment of the present invention.

MODE FOR INVENTION

Universal mobile telecommunications system (UMTS) is a 3rd Generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). The long-term evolution (LTE) of UMTS is under discussion by the3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3G LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

Hereinafter, structures, operations, and other features of the presentinvention will be readily understood from the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Embodiments described later are examples in which technicalfeatures of the present invention are applied to a 3GPP system.

Although the embodiments of the present invention are described using along term evolution (LTE) system and a LTE-advanced (LTE-A) system inthe present specification, they are purely exemplary. Therefore, theembodiments of the present invention are applicable to any othercommunication system corresponding to the above definition. In addition,although the embodiments of the present invention are described based ona frequency division duplex (FDD) scheme in the present specification,the embodiments of the present invention may be easily modified andapplied to a half-duplex FDD (H-FDD) scheme or a time division duplex(TDD) scheme.

FIG. 2A is a block diagram illustrating network structure of an evolveduniversal mobile telecommunication system (E-UMTS). The E-UMTS may bealso referred to as an LTE system. The communication network is widelydeployed to provide a variety of communication services such as voice(VoIP) through IMS and packet data.

As illustrated in FIG. 2A, the E-UMTS network includes an evolved UMTSterrestrial radio access network (E-UTRAN), an Evolved Packet Core (EPC)and one or more user equipment. The E-UTRAN may include one or moreevolved NodeB (eNodeB) 20, and a plurality of user equipment (UE) 10 maybe located in one cell. One or more E-UTRAN mobility management entity(MME)/system architecture evolution (SAE) gateways 30 may be positionedat the end of the network and connected to an external network.

As used herein, “downlink” refers to communication from eNodeB 20 to UE10, and “uplink” refers to communication from the UE to an eNodeB. UE 10refers to communication equipment carried by a user and may be alsoreferred to as a mobile station (MS), a user terminal (UT), a subscriberstation (SS) or a wireless device.

FIG. 2B is a block diagram depicting architecture of a typical E-UTRANand a typical EPC.

As illustrated in FIG. 2B, an eNodeB 20 provides end points of a userplane and a control plane to the UE 10. MME/SAE gateway 30 provides anend point of a session and mobility management function for UE 10. TheeNodeB and MME/SAE gateway may be connected via an S1 interface.

The eNodeB 20 is generally a fixed station that communicates with a UE10, and may also be referred to as a base station (BS) or an accesspoint. One eNodeB 20 may be deployed per cell. An interface fortransmitting user traffic or control traffic may be used between eNodeBs20.

The MME provides various functions including NAS signaling to eNodeBs20, NAS signaling security, AS Security control, Inter CN node signalingfor mobility between 3GPP access networks, Idle mode UE Reachability(including control and execution of paging retransmission), TrackingArea list management (for UE in idle and active mode), PDN GW andServing GW selection, MME selection for handovers with MME change, SGSNselection for handovers to 2G or 3G 3GPP access networks, Roaming,Authentication, Bearer management functions including dedicated bearerestablishment, Support for PWS (which includes ETWS and CMAS) messagetransmission. The SAE gateway host provides assorted functions includingPer-user based packet filtering (by e.g. deep packet inspection), LawfulInterception, UE IP address allocation, Transport level packet markingin the downlink, UL and DL service level charging, gating and rateenforcement, DL rate enforcement based on APN-AMBR. For clarity MME/SAEgateway 30 will be referred to herein simply as a “gateway,” but it isunderstood that this entity includes both an MME and an SAE gateway.

A plurality of nodes may be connected between eNodeB 20 and gateway 30via the S1 interface. The eNodeBs 20 may be connected to each other viaan X2 interface and neighboring eNodeBs may have a meshed networkstructure that has the X2 interface.

As illustrated, eNodeB 20 may perform functions of selection for gateway30, routing toward the gateway during a Radio Resource Control (RRC)activation, scheduling and transmitting of paging messages, schedulingand transmitting of Broadcast Channel (BCCH) information, dynamicallocation of resources to UEs 10 in both uplink and downlink,configuration and provisioning of eNodeB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE-IDLE state management,ciphering of the user plane, System Architecture Evolution (SAE) bearercontrol, and ciphering and integrity protection of Non-Access Stratum(NAS) signaling.

The EPC includes a mobility management entity (MME), a serving-gateway(S-GW), and a packet data network-gateway (PDN-GW). The MME hasinformation about connections and capabilities of UEs, mainly for use inmanaging the mobility of the UEs. The S-GW is a gateway having theE-UTRAN as an end point, and the PDN-GW is a gateway having a packetdata network (PDN) as an end point.

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a UE and an E-UTRAN based on a 3GPP radioaccess network standard. The control plane refers to a path used fortransmitting control messages used for managing a call between the UEand the E-UTRAN. The user plane refers to a path used for transmittingdata generated in an application layer, e.g., voice data or Internetpacket data.

A physical (PHY) layer of a first layer provides an information transferservice to a higher layer using a physical channel. The PHY layer isconnected to a medium access control (MAC) layer located on the higherlayer via a transport channel. Data is transported between the MAC layerand the PHY layer via the transport channel. Data is transported betweena physical layer of a transmitting side and a physical layer of areceiving side via physical channels. The physical channels use time andfrequency as radio resources. In detail, the physical channel ismodulated using an orthogonal frequency division multiple access (OFDMA)scheme in downlink and is modulated using a single carrier frequencydivision multiple access (SC-FDMA) scheme in uplink.

The MAC layer of a second layer provides a service to a radio linkcontrol (RLC) layer of a higher layer via a logical channel. The RLClayer of the second layer supports reliable data transmission. Afunction of the RLC layer may be implemented by a functional block ofthe MAC layer. A packet data convergence protocol (PDCP) layer of thesecond layer performs a header compression function to reduceunnecessary control information for efficient transmission of anInternet protocol (IP) packet such as an IP version 4 (IPv4) packet oran IP version 6 (IPv6) packet in a radio interface having a relativelysmall bandwidth.

A radio resource control (RRC) layer located at the bottom of a thirdlayer is defined only in the control plane. The RRC layer controlslogical channels, transport channels, and physical channels in relationto configuration, re-configuration, and release of radio bearers (RBs).An RB refers to a service that the second layer provides for datatransmission between the UE and the E-UTRAN. To this end, the RRC layerof the UE and the RRC layer of the E-UTRAN exchange RRC messages witheach other.

One cell of the eNB is set to operate in one of bandwidths such as 1.25,2.5, 5, 10, 15, and 20 MHz and provides a downlink or uplinktransmission service to a plurality of UEs in the bandwidth. Differentcells may be set to provide different bandwidths.

Downlink transport channels for transmission of data from the E-UTRAN tothe UE include a broadcast channel (BCH) for transmission of systeminformation, a paging channel (PCH) for transmission of paging messages,and a downlink shared channel (SCH) for transmission of user traffic orcontrol messages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted through the downlink SCH and mayalso be transmitted through a separate downlink multicast channel (MCH).

Uplink transport channels for transmission of data from the UE to theE-UTRAN include a random access channel (RACH) for transmission ofinitial control messages and an uplink SCH for transmission of usertraffic or control messages. Logical channels that are defined above thetransport channels and mapped to the transport channels include abroadcast control channel (BCCH), a paging control channel (PCCH), acommon control channel (CCCH), a multicast control channel (MCCH), and amulticast traffic channel (MTCH).

FIG. 4 is a view showing an example of a physical channel structure usedin an E-UMTS system. A physical channel includes several subframes on atime axis and several subcarriers on a frequency axis. Here, onesubframe includes a plurality of symbols on the time axis. One subframeincludes a plurality of resource blocks and one resource block includesa plurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use certain subcarriers of certain symbols (e.g., a firstsymbol) of a subframe for a physical downlink control channel (PDCCH),that is, an L1/L2 control channel. In FIG. 4, an L1/L2 controlinformation transmission area (PDCCH) and a data area (PDSCH) are shown.In one embodiment, a radio frame of 10 ms is used and one radio frameincludes 10 subframes. In addition, one subframe includes twoconsecutive slots. The length of one slot may be 0.5 ms. In addition,one subframe includes a plurality of OFDM symbols and a portion (e.g., afirst symbol) of the plurality of OFDM symbols may be used fortransmitting the L1/L2 control information. A transmission time interval(TTI) which is a unit time for transmitting data is 1 ms.

A base station and a UE mostly transmit/receive data via a PDSCH, whichis a physical channel, using a DL-SCH which is a transmission channel,except a certain control signal or certain service data. Informationindicating to which UE (one or a plurality of UEs) PDSCH data istransmitted and how the UE receive and decode PDSCH data is transmittedin a state of being included in the PDCCH.

For example, in one embodiment, a certain PDCCH is CRC-masked with aradio network temporary identity (RNTI) “A” and information about datais transmitted using a radio resource “B” (e.g., a frequency location)and transmission format information “C” (e.g., a transmission blocksize, modulation, coding information or the like) via a certainsubframe. Then, one or more UEs located in a cell monitor the PDCCHusing its RNTI information. And, a specific UE with RNTI “A” reads thePDCCH and then receive the PDSCH indicated by B and C in the PDCCHinformation.

FIG. 5 is an example of default data path for communication between twoUEs. With reference to FIG. 5, even when two UEs (e.g., UE1, UE2) inclose proximity communicate with each other, their data path (userplane) goes via the operator network. Thus a typical data path for thecommunication involves eNB(s) and/or Gateway(s) (GW(s)) (e.g., SGW/PGW).

FIGS. 6 and 7 are examples of data path scenarios for a proximitycommunication. If wireless devices (e.g., UE1, UE2) are in proximity ofeach other, they may be able to use a direct mode data path (FIG. 6) ora locally routed data path (FIG. 7). In the direct mode data path,wireless devices are connected directly each other (after appropriateprocedure(s), such as authentication), without eNB and SGW/PGW. In thelocally routed data path, wireless devices are connected each otherthrough eNB only.

FIG. 8 is a conceptual diagram illustrating for a non-roaming referencearchitecture.

PC1 to PC 5 represent interfaces. PC1 is a reference point between aProSe application in a UE and a ProSe App server. It is used to defineapplication level signaling requirements. PC 2 is a reference pointbetween the ProSe App Server and the ProSe Function. It is used todefine the interaction between ProSe App Server and ProSe functionalityprovided by the 3GPP EPS via ProSe Function. One example may be forapplication data updates for a ProSe database in the ProSe Function.Another example may be data for use by ProSe App Server in interworkingbetween 3GPP functionality and application data, e.g. name translation.PC3 is a reference point between the UE and ProSe Function. It is usedto define the interaction between UE and ProSe Function. An example maybe to use for configuration for ProSe discovery and communication. PC4is a reference point between the EPC and ProSe Function. It is used todefine the interaction between EPC and ProSe Function. Possible usecases may be when setting up a one-to-one communication path between UEsor when validating ProSe services (authorization) for session managementor mobility management in real time.

PC5 is a reference point between UE to UE used for control and userplane for discovery and communication, for relay and one-to-onecommunication (between UEs directly and between UEs over LTE-Uu).Lastly, PC6 is a reference point may be used for functions such as ProSeDiscovery between users subscribed to different PLMNs.

EPC (Evolved Packet Core) includes entities such as MME, S-GW, P-GW,PCRF, HSS etc. The EPC here represents the E-UTRAN Core Networkarchitecture. Interfaces inside the EPC may also be impacted albeit theyare not explicitly shown in FIG. 8.

Application servers, which are users of the ProSe capability forbuilding the application functionality, e.g. in the Public Safety casesthey can be specific agencies (PSAP) or in the commercial cases socialmedia. These applications are defined outside the 3GPP architecture butthere may be reference points towards 3GPP entities. The Applicationserver can communicate towards an application in the UE.

Applications in the UE use the ProSe capability for building theapplication functionality. Example may be for communication betweenmembers of Public Safety groups or for social media application thatrequests to find buddies in proximity. The ProSe Function in the network(as part of EPS) defined by 3GPP has a reference point towards the ProSeApp Server, towards the EPC and the UE.

The functionality may include but not restricted to e.g.:

Interworking via a reference point towards the 3rd party Applications

Authorization and configuration of the UE for discovery and Directcommunication

Enable the functionality of the EPC level ProSe discovery

ProSe related new subscriber data and /handling of data storage; alsohandling of ProSe identities;

Security related functionality

Provide Control towards the EPC for policy related functionality

Provide functionality for charging (via or outside of EPC, e.g. offlinecharging)

Especially, the following identities are used for ProSe DirectCommunication:

Source Layer-2 ID identifies a sender of a D2D packet at PC5 interface.The Source Layer-2 ID is used for identification of the receiver RLC UMentity;

Destination Layer-2 ID identifies a target of the D2D packet at PC5interface. The Destination Layer-2 ID is used for filtering of packetsat the MAC layer. The Destination Layer-2 ID may be a broadcast,groupcast or unicast identifier; and

SA L1 ID identifier in Scheduling Assignment (SA) at PC5 interface. SAL1 ID is used for filtering of packets at the physical layer. The SA L1ID may be a broadcast, groupcast or unicast identifier.

No Access Stratum signaling is required for group formation and toconfigure Source Layer-2 ID and Destination Layer-2 ID in the UE. Thisinformation is provided by higher layers.

In case of groupcast and unicast, the MAC layer will convert the higherlayer ProSe ID (i.e. ProSe Layer-2 Group ID and ProSe UE ID) identifyingthe target (Group, UE) into two bit strings of which one can beforwarded to the physical layer and used as SA L1 ID whereas the otheris used as Destination Layer-2 ID. For broadcast, L2 indicates to L1that it is a broadcast transmission using a pre-defined SA L1 ID in thesame format as for group- and unicast.

FIG. 9 is a conceptual diagram illustrating for a Layer 2 structure forSidelink. The Sidelink is UE to UE interface for ProSe directcommunication and ProSe Direct Discovery. Correspond to the PC5interface. The Sidelink comprises ProSe Direct Discovery and ProSeDirect Communication between UEs. The Sidelink uses uplink resources andphysical channel structure similar to uplink transmissions. However,some changes, noted below, are made to the physical channels. E-UTRAdefines two MAC entities; one in the UE and one in the E-UTRAN. TheseMAC entities handle the following transport channels additionally, i)sidelink broadcast channel (SL-BCH), ii) sidelink discovery channel(SL-DCH) and iii) sidelink shared channel (SL-SCH).

Basic transmission scheme: the Sidelink transmission uses the same basictransmission scheme as the UL transmission scheme. However, sidelink islimited to single cluster transmissions for all the sidelink physicalchannels. Further, sidelink uses a 1 symbol gap at the end of eachsidelink sub-frame.

Physical-layer processing: the Sidelink physical layer processing oftransport channels differs from UL transmission in the following steps:

i) Scrambling: for PSDCH and PSCCH, the scrambling is not UE-specific;

ii) Modulation: 64 QAM is not supported for Sidelink.

Physical Sidelink control channel: PSCCH is mapped to the Sidelinkcontrol resources. PSCCH indicates resource and other transmissionparameters used by a UE for PS SCH.

Sidelink reference signals: for PSDCH, PSCCH and PSSCH demodulation,reference signals similar to uplink demodulation reference signals aretransmitted in the 4th symbol of the slot in normal CP and in the 3rdsymbol of the slot in extended cyclic prefix. The Sidelink demodulationreference signals sequence length equals the size (number ofsub-carriers) of the assigned resource. For PSDCH and PSCCH, referencesignals are created based on a fixed base sequence, cyclic shift andorthogonal cover code.

Physical channel procedure: for in-coverage operation, the powerspectral density of the sidelink transmissions can be influenced by theeNB.

FIG. 10a is a conceptual diagram illustrating for User-Plane protocolstack for ProSe Direct Communication, and FIG. 10b is Control-Planeprotocol stack for ProSe Direct Communication.

FIG. 10a shows the protocol stack for the user plane, where PDCP, RLCand MAC sublayers (terminate at the other UE) perform the functionslisted for the user plane (e.g. header compression, HARQretransmissions). The PC5 interface consists of PDCP, RLC, MAC and PHYas shown in FIG. 10 a.

User plane details of ProSe Direct Communication: i) MAC sub headercontains LCIDs (to differentiate multiple logical channels), ii) The MACheader comprises a Source Layer-2 ID and a Destination Layer-2 ID, iii)At MAC Multiplexing/demultiplexing, priority handling and padding areuseful for ProSe Direct communication, iv) RLC UM is used for ProSeDirect communication, v) Segmentation and reassembly of RLC SDUs areperformed, vi) A receiving UE needs to maintain at least one RLC UMentity per transmitting peer UE, vii) An RLC UM receiver entity does notneed to be configured prior to reception of the first RLC UM data unit,and viii) U-Mode is used for header compression in PDCP for ProSe DirectCommunication.

FIG. 10b shows the protocol stack for the control plane, where RRC, RLC,MAC, and PHY sublayers (terminate at the other UE) perform the functionslisted for the control plane. A D2D UE does not establish and maintain alogical connection to receiving D2D UEs prior to a D2D communication.

FIG. 11 is a conceptual diagram illustrating for a PC5 interface forProSe Direct Discovery.

ProSe Direct Discovery is defined as the procedure used by theProSe-enabled UE to discover other ProSe-enabled UE(s) in its proximityusing E-UTRA direct radio signals via PC5.

Radio Protocol Stack (AS) for ProSe Direct Discovery is shown in FIG.11.

The AS layer performs the following functions:

Interfaces with upper layer (ProSe Protocol): The MAC layer receives thediscovery information from the upper layer (ProSe Protocol). The IPlayer is not used for transmitting the discovery information.

Scheduling: The MAC layer determines the radio resource to be used forannouncing the discovery information received from upper layer.

Discovery PDU generation: The MAC layer builds the MAC PDU carrying thediscovery information and sends the MAC PDU to the physical layer fortransmission in the determined radio resource. No MAC header is added.

There are two types of resource allocation for discovery informationannouncement.

Type 1: A resource allocation procedure where resources for announcingof discovery information are allocated on a non UE specific basis,further characterized by: i) The eNB provides the UE(s) with theresource pool configuration used for announcing of discoveryinformation. The configuration may be signalled in SIB, ii) The UEautonomously selects radio resource(s) from the indicated resource pooland announce discovery information, iii) The UE can announce discoveryinformation on a randomly selected discovery resource during eachdiscovery period.

Type 2: A resource allocation procedure where resources for announcingof discovery information are allocated on a per UE specific basis,further characterized by: i) The UE in RRC_CONNECTED may requestresource(s) for announcing of discovery information from the eNB viaRRC, ii) The eNB assigns resource(s) via RRC, iii) The resources areallocated within the resource pool that is configured in UEs formonitoring.

For UEs in RRC_IDLE, the eNB may select one of the following options:

The eNB may provide a Type 1 resource pool for discovery informationannouncement in SIB. UEs that are authorized for Prose Direct Discoveryuse these resources for announcing discovery information in RRC_IDLE.

The eNB may indicate in SIB that it supports D2D but does not provideresources for discovery information announcement. UEs need to enter RRCConnected in order to request D2D resources for discovery informationannouncement.

For UEs in RRC_CONNECTED,

A UE authorized to perform ProSe Direct Discovery announcement indicatesto the eNB that it wants to perform D2D discovery announcement.

The eNB validates whether the UE is authorized for ProSe DirectDiscovery announcement using the UE context received from MME.

The eNB may configure the UE to use a Type 1 resource pool or dedicatedType 2 resources for discovery information announcement via dedicatedRRC signaling (or no resource).

The resources allocated by the eNB are valid until a) the eNBde-configures the resource(s) by RRC signaling or b) the UE enters IDLE.(FFS whether resources may remain valid even in IDLE).

Receiving UEs in RRC_IDLE and RRC_CONNECTED monitor both Type 1 and Type2 discovery resource pools as authorized. The eNB provides the resourcepool configuration used for discovery information monitoring in SIB. TheSIB may contain discovery resources used for announcing in neighborcells as well.

Recently, the extension of network coverage using L3-based UE-to-NetworkRelay is expected to be supported. When the UE starts ProSecommunication within the network and then moves out of the coverage, therelay may be selected by the UE or the network for service coverageextension. During changing the traffic path of the (potential) remote UEfrom eNB to a relay, there could be service interruption if the relayingservice activation (including relay selection) for the remote UE isperformed too late. On the contrary, if the relaying service activationis performed early, the remote UE might have dual connectivity for thesame (or different) PDN connection(s) where one connectivity goesthrough the eNB and another goes through relay. In addition, the(potential) UE may establish unnecessary connection between relay.

FIG. 12 is a conceptual diagram illustrating for one example of awireless Communication system supporting ProSe Direct Communicationaccording to one embodiment of the present invention.

Referring FIG. 12, a wireless Communication system supporting ProSeDirect Communication includes eNodeB 1210, relay 1220, and remote UE1230. According to one embodiment, the remote UE 1230 may be served bythe relay 1220 when staying out of coverage is going toward cell bordersatisfying s-criterion (in-coverage). It is assumed that the remote UE1230 is currently served by relay 1220 which is within the cell. Amethod for disconnecting the D2D link connection between the remote UE1230 and the relay 1220 may be defined as follows.

FIGS. 13-15 show an example of a method for disconnecting a D2D linkconnection according to an embodiment of the present invention.

Referring to FIG. 13, the remote UE (1320) may establish a radioresource control (RRC) connection with a cell (1310) according to apredetermined condition (S1351). For example, if the remote UE (1320) isin the RRC idle mode, the remote UE (1320) establishes the RRCconnection when the predetermined condition is satisfied.

As an example, the predetermined condition may be related to a channelquality. For example, the remote UE (1320) may receive a threshold valueand measure a channel quality between the remote UE (1320) and the cell(1310). The channel quality may be a RSRP or RSRQ. Subsequently, if ameasured channel quality is equal to or higher than the threshold value,the remote UE (1320) may attempt to establish the RRC connection thecell (1310). The threshold value may be a value bigger than thethreshold values for S-criterion.

For another example, if the measured RSRP/RSRQ value−hysteresis>theconfigured RSRP/RSRQ threshold, the entering condition is triggered andentering procedure is performed by the remote UE (1320). In contrast, ifthe measured RSRP/RSRQ value+hysteresis<the configured RSRP/RSRQthreshold, leaving condition is triggered and leaving procedure isperformed by the remote UE (1320).

As another example, predetermined condition for establishing a RRC maybe as follows: i) if a cell satisfy S-criterion, ii) if the UE's servingcell is suitable, iii) if the UE's serving cell fulfils the conditionsto support sidelink direct communication in limited service state asspecified in TS 23.303 section 4.5.6 and the UE is in RRC_IDLE, iv) ifthe serving cell connected with the relay is different from the servingcell connected with the remote UE, and v) if the cell connected with therelay for ProSe/MBMS is different from the cell connected with theremote UE for ProSe/MBMS.

The threshold is fixed or provided in broadcast signaling or dedicatedsignaling. If the threshold is provided in dedicated/broadcastsignaling, the validity information also is provided. The validityinformation may include:

i) Time information: When the validity information is received or the UEtransits to RRC idle state, the UE sets the timer with the valueincluded in validity information. Alternatively, the UE sets the timerwith the value included in validity information upon receiving theinformation. If the timer is expired, the UE considers the configuredthreshold invalid. During the timer is running, the UE considers theconfigured threshold valid.

ii) Area information: Area information includes the list of cellidentities, tracking area identities, PLMN IDs. When the UE in the areaidentified by area information, the UE considers the configuredthreshold valid.

iii) The time information and area information: In this case, timecondition and area condition is met, the UE considers the configuredthreshold valid. Otherwise, the UE considers the configured thresholdinvalid.

When the RRC connection is established, the remote UE (1320) transmits areporting message on the D2D link connection to the cell (S1353). As anexample, the reporting message may include at least one of L2 identityof the remote UE (e.g. ProSe UE ID), an identity of the relay UE, anidentity of the cell connected with the relay UE, an indicatorindicating whether to disconnect the D2D link connection, an indicatorindicating whether the remote UE is currently served by the relay UE,serving cell quality of the remote UE and the corresponding serving cellidentity.

Subsequently, the cell (1310) may determine whether the cell connectedwith the remote UE and a cell connected with the relay UE are same. Forexample, the identity of the cell connected with the relay UE may beused for determining.

As an example, if the cell connected with the remote UE and the cellconnected with the relay UE are different, the cell connected with theremote UE may send a request message to request disconnection of the D2Dlink connection between the remote UE (1320) and the relay UE (1330) tothe cell (1340) (S1355). The request message may include the L2 relayidentity and remote UE identity (e.g. ProSe UE id).

Subsequently, the cell (1340) may send a disconnection message torequest disconnection of the D2D link connection between the relay UE(1330) and remote UE (1320) (S1357). The disconnection message mayinclude the remote UE identity. The relay UE (1330) receiveddisconnection message may send a request message to the remote UE(S1359). The request message may be transmitted over PC5 interface tothe remote UE (1320).

When the remote UE (1320) receive the request message, the remote UE(1320) may perform an operation for disconnecting the D2D linkconnection according to the request message and may transmit a responsemessage to the relay UE (1330). The response message may be transmittedover PC5 interface to the relay UE (1330).

As another example, referring to FIG. 14, the remote UE (1420) mayestablish a radio resource control (RRC) connection with a cell (1410)according to a predetermined condition (S1451). After the RRC connectionis established, the remote UE (1420) transmits a reporting message onthe D2D link connection to the cell (1410) (S1453). And, the cell (1410)may send a request message to request disconnection of the D2D linkconnection to the cell (1440) (S1455) and may receive the responsemessage from the cell (1440) in response to the request message (S1457).Detailed description repeated with the description of FIG. 13 will beomitted.

Subsequently, the cell (1410) may send a disconnection message torequest disconnection of the D2D link connection to the remote UE (1420)(S1459). After that, the remote UE (1420) may send a request message tothe relay UE (S1461). The request message may be transmitted over PC5interface to the relay UE (1430).

When the relay UE (1430) receive the request message, the relay UE(1430) may perform an operation for disconnecting the D2D linkconnection according to the request message and transmit a responsemessage to the remote UE (1420). The response message may be transmittedover PC5 interface to the remote UE (1420).

As another example, the cell connected with the remote UE and the cellconnected with the relay UE (1330) may be same. Referring to FIG. 15,the remote UE (1520) may establish a radio resource control (RRC)connection with a cell (1510) according to a predetermined condition(S1551). After the RRC connection is established, the remote UE (1520)transmits a reporting message on the D2D link connection to the cell(1510) (S1553). Detailed description repeated with the description ofFIG. 13 will be omitted.

Subsequently, the cell (1510) may send a disconnection message torequest disconnection of the D2D link connection to the remote UE (1520)(S1555). After that, the remote UE (1520) may send a request message tothe relay UE (S1557). The request message may be transmitted over PC5interface to the relay UE (1530).

When the relay UE (1530) receive the request message, the relay UE(1530) may perform an operation for disconnecting the D2D linkconnection according to the request message and may transmit a responsemessage to the remote UE (1520). The response message may be transmittedover PC5 interface to the remote UE (1520).

As another example, the remote UE may disconnect the D2D link connectionautonomously. If the predetermined condition is satisfied, the remote UEmay send a disconnect request message to the relay UE. The requestmessage may be transmitted over PC5 interface to the relay UE. Inaddition, the remote UE may establish a radio resource controlconnection with a cell when the predetermined condition is satisfied.

FIG. 16 is a block diagram for one example of a communication deviceaccording to one embodiment of the present invention.

Referring to FIG. 16, a communication device 1600 includes a processor1610, a memory 1620, an RF module 1630, a display module 1640 and a userinterface module 1650.

The communication device 1600 is illustrated for clarity and convenienceof the description and some modules can be omitted. Moreover, thecommunication device 1600 is able to further include at least onenecessary module. And, some modules of the communication device 1600 canbe further divided into sub-modules. The processor 1610 is configured toperform operations according to the embodiment of the present inventionexemplarily described with reference to the accompanying drawings. Inparticular, the detailed operations of the processor 1610 can refer tothe contents described with reference to FIGS. 1 to 15.

The memory 1620 is connected to the processor 1610 and stores operatingsystems, applications, program codes, data and the like. The RF module1630 is connected to the processor 1610 and performs a function ofconverting a baseband signal to a radio signal or converting a radiosignal to a baseband signal. For this, the RF module 1630 performsanalog conversion, amplification, filtering and frequency uplinktransform or inverse processes thereof. The display module 1640 isconnected to the processor 1610 and displays various kinds ofinformation. The display module 1640 can include such a well-knownelement as LCD (Liquid Crystal Display), LED (Light Emitting Diode),OLED (Organic Light Emitting Diode) and the like, by which the presentinvention is non-limited. The user interface module 1650 is connected tothe processor 1610 and can include a combination of well-knowninterfaces including a keypad, a touchscreen and the like.

The above-described embodiments correspond to combination of elementsand features of the present invention in prescribed forms. And, it isable to consider that the respective elements or features are selectiveunless they are explicitly mentioned. Each of the elements or featurescan be implemented in a form failing to be combined with other elementsor features. Moreover, it is able to implement an embodiment of thepresent invention by combining elements and/or features together inpart. A sequence of operations explained for each embodiment of thepresent invention can be modified. Some configurations or features ofone embodiment can be included in another embodiment or can besubstituted for corresponding configurations or features of anotherembodiment. It is apparent that an embodiment can be configured bycombining claims, which are not explicitly cited in-between, togetherwithout departing from the spirit and scope of ‘what is claimed is’ orthat those claims can be included as new claims by revision after filingan application.

In this disclosure, a specific operation explained as performed by abase station can be performed by an upper node of the base station insome cases. In particular, in a network constructed with a plurality ofnetwork nodes including a base station, it is apparent that variousoperations performed for communication with a terminal can be performedby a base station or other network nodes except the base station. Inthis case, ‘base station’ can be replaced by such a terminology as afixed station, a Node B, an eNode B (eNB), an access point and the like.

Embodiments of the present invention can be implemented using variousmeans. For instance, embodiments of the present invention can beimplemented using hardware, firmware, software and/or any combinationsthereof. In case of the implementation by hardware, a method accordingto one embodiment of the present invention can be implemented by atleast one selected from the group consisting of ASICs (applicationspecific integrated circuits), DSPs (digital signal processors), DSPDs(digital signal processing devices), PLDs (programmable logic devices),FPGAs (field programmable gate arrays), processor, controller,microcontroller, microprocessor and the like.

In case of the implementation by firmware or software, a methodaccording to each embodiment of the present invention can be implementedby modules, procedures, and/or functions for performing theabove-explained functions or operations. Software code is stored in amemory unit and is then drivable by a processor. The memory unit isprovided within or outside the processor to exchange data with theprocessor through the various means known in public.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents.

INDUSTRIAL APPLICABILITY

While the above-described method has been described centering on anexample applied to the 3GPP LTE system, the present invention isapplicable to a variety of wireless communication systems in addition tothe 3GPP LTE system.

What is claimed is:
 1. A method for disconnecting, by a remote userequipment (UE), a device to device (D2D) link connection with a relay UEin a wireless communication system, the method comprising: establishinga radio resource control (RRC) connection with a cell; transmitting, tothe cell connected with the remote UE, a reporting message on the D2Dlink connection; if the cell connected with the remote UE and a cellconnected with the relay UE are different, receiving, from the relay UE,a first request message for disconnecting the D2D link connection withthe relay UE in response to the reporting message; and disconnecting theD2D link connection according to the first request message.
 2. Themethod of claim 1, wherein the RRC connection with the cell isestablished when a quality of a channel between the remote UE and thecell is higher than a threshold value.
 3. The method of claim 1, whereinthe reporting message including at least one of an identity of theremote UE, an identity of the relay UE, an identity of the cellconnected with the relay UE, an indicator indicating whether todisconnect the D2D link connection, an indicator indicating whether theremote UE is currently served by the relay UE and serving cell qualityof the remote UE.
 4. The method of claim 1, the method furthercomprising: if the cell connected with the remote UE and the cellconnected with the relay UE are same, receiving a first disconnectionmessage, from the cell connected with the remote UE, for disconnectingthe D2D link connection in response to the reporting message; anddisconnecting the D2D link connection according to the firstdisconnection message.
 5. The method of claim 1, wherein the firstrequest message is transmitted from the relay UE based on a seconddisconnection message on the cell connected with the relay UE, andwherein the second disconnection message is transmitted from the cellconnected with the relay UE to the relay UE based on a second requestmessage on the cell connected with the remote UE.
 6. The method of claim5, wherein the second request message is transmitted from the cellconnected with the remote UE to the cell connected with the relay UE,and wherein the second request message includes an identity of theremote UE and an identity of the relay UE.
 7. The method of claim 5,wherein the second disconnection message includes an identity of theremote UE.
 8. A user equipment (UE) connected with a relay UE through adevice to device (D2D) link in a wireless communication system, the UEcomprising: a radio frequency (RF) module configured to transmit/receivesignals; and a processor configured to process the signals, wherein theprocessor is configured to establish a radio resource control (RRC)connection with a cell, control the RF modul to transmit, to the cellconnected with the remote UE, a reporting message on the D2D linkconnection, if the cell connected with the remote UE and a cellconnected with the relay UE are different, control the RF modul toreceive, from the relay UE, a first request message for disconnectingthe D2D link connection with the relay UE in response to the reportingmessage, and disconnect the D2D link connection according to the firstrequest message.
 9. The UE of claim 8, wherein the RRC connection withthe cell is established when a quality of a channel between the remoteUE and the cell is higher than a threshold value.
 10. The UE of claim 8,wherein the reporting message including at least one of an identity ofthe remote UE, an identity of the relay UE, an identity of the cellconnected with the relay UE, an indicator indicating whether todisconnect the D2D link connection, an indicator indicating whether theremote UE is currently served by the relay UE and serving cell qualityof the remote UE.
 11. The UE of claim 8, wherein the processor isfurther configured to: if the cell connected with the remote UE and thecell connected with the relay UE are same, control the RF modul toreceive a first disconnection message, from the cell connected with theremote UE, for disconnecting the D2D link connection in response to thereporting message, and disconnect the D2D link connection according tothe first disconnection message.
 12. The UE of claim 8, wherein thefirst request message is transmitted from the relay UE based on a seconddisconnection message on the cell connected with the relay UE, andwherein the second disconnection message is transmitted from the cellconnected with the relay UE to the relay UE based on a second requestmessage on the cell connected with the remote UE.
 13. The UE of claim12, wherein the second request message is transmitted from the cellconnected with the remote UE to the cell connected with the relay UE,and wherein the second request message includes an identity of theremote UE and an identity of the relay UE.
 14. The UE of claim 12,wherein the second disconnection message includes an identity of theremote UE.